Watch the Classic Ballad online guitar lesson by Vicki Genfan from 30 Strumming Patterns You MUST Know
I'm using a G-D-Am-C progression here. Because I'm using it at a slow tempo, I'm playing 16th notes and this gives the progression a lot of movement and energy. It also fills up a lot of space. If you're using it in a song you might play around with making some breaks or stops somewhere in the song just for a variation or for bringing attention to an important lyric or hook.
Pay close attention here to the accented beats. I've found this pattern works well in many different tempos. Give it a try and see/feel where you like it and what ideas it inspires at different speeds.